Sticker



FIG. 1 is a front view of a sticker of my design.

FIG. 2 is a back view of the sticker thereof; and,

FIG. 3 is a left side view of the sticker thereof, the right side view, top view, and bottom view being identical.

The dashed lines in the drawings illustrate portions that form no part of the claimed design. 

CLAIM The ornamental design for a sticker, as shown and described. 